1. Field of the Invention
The present invention relates to liquid crystal displays, and in particular to a liquid crystal display panel that includes two thin film transistors in each of pixel units thereof, the two thin film transistors having different Channel width/length ratios.
2. General Background
Liquid crystal displays (LCDs) generally have the advantages of lightness in weight, a thin profile, flexible sizing, and low power consumption. For these reasons, LCDs are widely used in products such as laptops, personal digital assistants, mobile phones, and so on. An LCD typically includes an LCD panel. The LCD panel is generally formed by an upper substrate, a lower substrate, and a liquid crystal layer interposed between the substrates.
A conventional LCD such as a twisted nematic (TN) LCD commonly has a rather limited viewing angle. Thus, a technique known as Multi-domain Vertical Alignment (MVA) has been developed. In an MVA-type LCD, each of pixel units of an LCD panel of the LCD is divided into at least two regions (domains) with a plurality of protrusions formed on both of the upper and lower substrates thereat. Liquid crystal molecules of the liquid crystal layer within each region have different pre-tilt angles according to the configurations of the protrusions. The result is that the viewing angle of the LCD is broadened. A means for driving the LCD includes using two thin film transistors (TFTs) in each pixel unit for respectively driving the two different regions of the pixel unit.
Referring to FIGS. 4 and 5, aspects of a conventional MVA-type LCD panel are illustrated. The LCD panel 100 includes a plurality of gate lines 101, first data lines 102, and second data lines 112. The first and second data lines 102, 112 are parallel to each other and arranged in alternating fashion. The first and second data lines 102, 112 are insulated from and cross the gate lines 101. Each of pixel units 108 is divided into an upper pixel area and a lower pixel area by a corresponding one of the gate lines 101 crossing through a middle portion of the pixel unit 108.
The upper pixel area includes a first thin film transistor (TFT) 103, a first pixel electrode 104, and a common electrode 105. The first TFT 103 includes a gate 1031, a source 1032, and a drain 1033. The gate 1031 connects to the gate line 101, the source 1032 connects to the first data line 102, and the drain 1033 connects to the first pixel electrode 104. The first pixel electrode 104 and the common electrode 105 define a first liquid crystal (LC) capacitor (not labeled) for controlling a tilt angle of liquid crystal molecules in a liquid crystal layer of the upper pixel area.
The lower pixel area includes a second TFT 113, a second pixel electrode 114, and the common electrode 105. The second TFT 113 includes a gate 1131, a source 1132, and a drain 1133. The gate 1131 connects to the gate line 101, the source 1132 connects to the second data line 112, and the drain 1133 connects to the second pixel electrode 114. Thus the gates 1031, 1131 of the first and second TFTs 103, 113 are connected to the same gate line 101 within the pixel unit 108. The second pixel electrode 114 and the common electrode 105 define a second LC capacitor (not labeled) for controlling a tilt angle of liquid crystal molecules in the liquid crystal layer of the lower pixel area.
FIGS. 6A and 6B show tilt angles of liquid crystal molecules in each of the upper and lower pixel areas respectively. Referring also to FIGS. 4 and 5, operation of the LCD panel 100 is as follows. Firstly, the gates 1031, 1131 of the first and second TFTs 103, 113 are enabled by the gate line 101. Thereby, the sources 1032, 1132 are connected to the drains 1033, 1133 respectively. Secondly, the first pixel electrode 104 is charged via a first signal transferred through the first data line 102, and the second pixel electrode 114 is charged via a second signal transferred through the second data line 112. Thirdly, tilt angles θ1 and θ2 of the liquid crystal molecules arranged in the upper and lower pixel areas respectively are determined by the electrical potentials of the first and second pixel electrodes 104, 114 respectively. The electrical potentials of the first and second pixel electrodes 104, 114 are different from each other. Therefore, the pixel unit 108 having two different tilt angles in the upper and lower pixel areas thereof respectively can be realized.
The LCD panel 100 needs to provide the two data lines 102, 112 for each of columns of the pixel units 108 arranged in the matrix of pixel units 108. Typically, the data lines 102, 112 are made of opaque material such as metallic material. Therefore the aperture ratio of the LCD panel 100 is rather low.
Accordingly, what is needed is an LCD configured to provide both MVA and a high aperture ratio.